This invention relates to flash memory program and erase operations.
There has been a recent trend toward increasing the speed of flash memory devices such as flash electrically erasable programmable read only memory (flash EEPROM) devices that are used in portable computers and other devices. Flash memory devices contain an array of memory cells which are utilized to store data. These devices contain charge pump circuitry for converting an input voltage to a high output voltage and current necessary for programming and erasing the data in the memory cells. The output voltage and current determine the output capacity of the charge pump.
One problem encountered during the process of manufacturing the charge pump circuitry is that the actual output capacity of the charge pump may vary from the optimal output capacity. Often, charge pumps that are produced lack sufficient output capacity to program and erase the memory cells. This results in an undesirable increase in the time to program and erase the cells and a decrease in throughput. Charge pumps also may produce excessive output capacity resulting in an increase in power consumption. Furthermore, once the flash memory devices are placed in an electronic device such as a portable computer, variations in input voltage and in temperature also may cause the output capacity of the charge pump to decrease or increase.